The present invention relates to knee braces. More particularly, the present invention relates to a knee brace having three point fixation with an extension cushion to relieve forces against the anterior cruciate ligament in response to extension of the leg.
As the leg extends toward its fully straightened position the anterior shifting force imposed by the quadriceps muscle on the tibia is counteracted by the anterior cruciate ligament to prevent the tibia from being anteriorly shifted away from its normal position relative to the femur. When the anterior cruciate ligament is damaged the quadriceps muscle causes an undesirable tibial shift. It is therefore desirable to counter the anterior force imposed by the quadriceps muscle by imposing a counteractive force on the tibia using a knee brace.
Not surprisingly, there have been numerous attempts to prevent and decrease damage to the anterior cruciate ligament. One such example is U.S. Pat. No. 4,955,369 to Bledsoe which discloses a dynamically shiftable knee brace used to counteract anterior tibial displacement caused during leg extension by the quadriceps muscle or when the anterior cruciate ligament is missing or damaged. The brace includes pairs of thigh and calf support members which extend along and are strapped to thigh and calf portions of the leg. The support member pairs are pivotally connected at their inner ends to one another by a pair of specially designed hinges positioned on opposite sides of the knee. As the leg is extended from a flexed position toward its fully straightened position the hinges cause a relative anterior-posterior shift between the support member pairs in a manner creating a shear force across the knee which is opposite that generated by the quadriceps muscle.
In another patent, U.S. Pat. No. 4,271,831 to Deibert, there is provided a knee brace which is hinged at the knee joint of the wearer and includes a hammock device for drawing the tibia forward into a desired position using a strap to encircle the tibia and secure the tibia in the desired position. This brace is particularly suitable for those with an injured posterior cruciate ligament.
When the ligaments around the knee have been damaged it is desirable to prevent the knee from hyperextending. One way to prevent hyperextension is to provide a mechanism to prevent the knee from entirely straightening out. In this regard, U.S. Pat. No. 4,732,143 to Kausek et al. discloses a knee brace having a selectable extension stop for a polycentric hinge which prevents the knee from straightening out. The hinge has a pair of rigid arms connected at spaced-apart pivotal connections between a pair of parallel face plates. Intermeshing gear teeth are provided on the mating ends of the arms causing simultaneous pivoting action of both arms about their pivotal connections with the plates. An extension stop of rigid material is provided to prevent hyperextension of the knee. The extension stop is a C-shaped plastic body which is attachable along one of the face plates. The extension stop includes a resilient clip for attaching the stop to one of the face plates and an extendable block at the opposing end positionable between the mating ends of the arms to limit the forward rotation of the arms. The difficulty with a knee brace of this type is that its use of a rigid extension stop does not allow for a soft cushioning of the knee as the leg reaches its desired extension.
U.S. Pat. No. 5,288,287 to Castillo et al. discloses another knee brace having thigh and calf frame members connected by a polycentric hinge. Attached to the inner surface of the lower frame member is a tibia pad which is used to provide a firm interface between the lower frame members and the portion of the knee joint adjacent the crest of the tibia. Means are provided to adjust the position of the tibia pad relative to the knee joint. This brace also includes a rigid extension stop.
The disadvantages of the prior art braces is the inability to dynamically deliver a post shear force countering displacement forces. There remains a need for a knee brace capable of providing a soft cushioning of the knee as the leg reaches its desired extension.